A spray pump has been described in German Democratic Republic Patent No. 58 944, in which the outlet valve is formed by a spherical valve body which is fixed on a long rod at the end of a piston sleeve. The piston sleeve rests against the valve body at its end remote from the pump chamber. The piston sleeve which is bowl-shaped at the pump chamber end is biased by the restoring spring of the pump and opens under the influence of the pressure of this spring and the liquid pressure by being lifted from the valve body. The piston sleeve applies a strong axial force on the valve body which consequently has to be mounted firmly on the rod. This is a difficult construction to produce. In order to mount the rod, the piston has to be designed in two parts. Moreover, the opening behaviour of this valve is not ideal since the opening force increases toward the end of the stroke due to the increasing spring force. Difficulties can therefore arise during closure of the valve at the end of the stroke.
A piston pump has also been described in German Pat. No. 13 02 372 in which the piston has a thin-walled neck which is axially compressed under the influence of the liquid pressure so that it opens the liquid valve. The valve body is rigidly mounted on a hollow piston rod. A spring force acts on the valve body so that the valve is opened only by the liquid pressure. This design operates quite satisfactorily with high reliability. However, it would be desirable to improve this spray pump by further simplifying production and mounting. In the known spray pump, for example, the initial closing force to which the resilient neck subjects the valve has to be maintained during production and mounting.